Higher levels of integration and improved processing technology produce increasingly complex integrated circuits. These new generations of integrated circuits often operate at higher frequencies and generate more heat than their predecessors. Typically, heat sinks, fans, and heat pipes are employed to dissipate heat from integrated circuits and other electronic components. Increases in heat generation are often accommodated by simply increasing the quantity or size of these heat dissipation elements. The relatively small size of a portable computing device, however, complicates heat dissipation by limiting airflow, crowding heat generating components, and reducing the space available for heat dissipation devices.
A portable computing device typically includes two computer housing members which are rotatably coupled by a hinge. The first member, a computer base, usually has an input device such as a keyboard or a touchpad as well as a number of electronic components. Integrated circuits with the highest clock frequency are typically located in close proximity to each other within the computer base. Accordingly, there is often a region in the base having a level of heat generation greater than that of the rest of the computer.
Since the computer base size is generally kept to a minimum, and the computer base contains both the input device and numerous other electronic components, there may be inadequate space to dissipate enough heat to keep the electronic components within their acceptable range of operating temperatures. Heat dissipation through the bottom of the base is limited because the computer is usually operated on a relatively flat surface. Also, the input device (e.g. keyboard) can limit the heat flow through the top of the base. Further, since a horizontal surface is less effective at producing convective air currents to dissipate heat than is a vertical surface, the traditional horizontal operating position adds to the difficulty of dissipating heat from the computer base.
The second member, the computer display, is typically in a substantially vertical position during computer operation. The display contains an output device such as a screen and some additional computer circuitry. In most computers, the screen and the other circuitry in the display do not generate more heat than can be dissipated given the surface area available and the relatively vertical position of the display. Thus, additional heat from the base could be dissipated in the display if transferred from the base to the display.
The main difficulty in transferring heat between the base and the display is that many efficient heat conductors such as heat pipes are not sufficiently flexible to accommodate the repetitive motion expected between the hinged base and display of a computing device. A traditional hinge, having a first and a second hinged surface each having a cylindrical portion forming a gudgeon (each gudgeon defining socket for the pin or pintle of the hinge) and a pintle (the pin on which the gudgeons turn) can transfer heat between the two hinged surfaces; however, the geometry and heat transfer capacity of a traditional hinge are not well suited for transferring heat between the base and display of a portable computing device. In a portable computing device, the region of highest heat generation is usually not immediately adjacent to, and therefore cannot be directly coupled to, a traditional hinge, thus reducing the ability to thermally couple the region of highest heat generation in the base to the display.
Heat transfer through a hinge is improved by increasing the hinge mass and by using more expensive, highly conductive materials, however, the increased weight and cost are seldom, justified. Such a prior art technique is discussed in "Low Torque Hinged Heat Transfer Joint" (U.S. Pat. No. 5,129,448) which proposes heat transfer from a first to a second flat surface of a hinge using numerous interleaved fingers having a special heat conductive low friction coating allowing maximal surface area contact. This technique which transfers heat between the rotatable flat surfaces of a hinge may be geometrically incompatible and undesirably heavy and expensive for use in some portable computing devices.